Progressive gear assemblies find application, for example, in vehicle steering systems, particularly for motor vehicles. It is usually the case that turning the steering wheel is communicated via a steering shaft to a gear wheel meshing with a gear rack. When driven in this way the gear wheel shifts the gear rack which positions the wheels accordingly. With a progressive steering or progressive gear assembly the translation ratio is reduced from a maximum value in a center range of the steering wheel when the steering wheel is turned. This means that in the straight-ahead position of the steering wheel a relatively large turn of the steering wheel produces a small change in direction of the driving track, whereas when maneuvering with the steering wheel already strongly turned, just a relatively small change in turn produces a large change in direction. This is particularly desirable when parking or negotiating a serpentine.
The prior art proposes various solutions for achieving a progressive response of the gear assembly. However, these gear assemblies are structured relatively complicated and are thus correspondingly expensive in manufacture and maintenance. It is also a drawback with gear assemblies comprising a multitude of components that they often exhibit an undesired backlash or that torque fluctuations have to be put up with. In addition to this, the reversing point is attained relatively early.
DE-A-1 146 769 discloses an automotive steering gear with a variable translation ratio, the gear assembly comprising a gear wheel and a gear rack. In this arrangement the gear wheel is configured non-round in an eccentric mounting.
DE-A-39 13 809 proposes a small angle steering device with a pair of elliptical gear wheels.